Method and means of grinding with electrophoretic assistance

ABSTRACT

A grinding system in which an electrically conductive workpiece is moved against and relative to a rotating grinding wheel, an electrode spaced from and electrically insulated from the workpiece, means to maintain the space between the workpiece and the electrode filled with an electrically substantially nonconducting coolant fluid containing electrically charged particles of a cutting fluid or other cutting agent, and a direct current power source connected to so charge the workpiece and the electrode that the charged particles of a cutting fluid or other cutting agent migrate to and form a film upon the surface of the workpiece as it passes beneath the grinding wheel.

United States Patent [191 Coes,Jr. l

[ METHOD AND MEANS OF GRINDING WITH ELECTROPHORETIC ASSISTANCE [75] Inventor: Loring Coes, Jr., Princeton, Mass.

Assignee: Norton Company, Worcester, Mass.

Filed: Mar. 27, 1973 Appl. No.: 345,310

US. Cl. 51/322 Int. Cl B24!) 1/00 Field of Search 51/84 R, 281 R, 316, 322,

[ 5 6] References Cited UNITED STATES PATENTS 3,548,549 12/1 970 Dunn ..5l/322X 3,747,284 7/1973 Lyccko ..5l/322X FOREIGN PATENTS OR APPLICATIONS 1,190,072 4/1970 GreatBritainu ..-...L. 51/322 in] 3,823,515 July 16, 1974 Primary Examiner -Donald G. Kelly Attorney, Agent, or Firm-Lewis M. Smith, Jr.

ABSTRACT A grinding system in which an electrically conductive workpiece is moved against and relative to a rotating grinding wheel, an electrode spaced from and electrically insulated from the workpiece, means to maintain the space between the workpiece and the electrode filled with an electrically substantially nonconducting coolant fluid containing electrically charged particles of a cutting fluid or other cutting agent, and a direct current power source connected to so charge the workpiece and the electrode that the charged particles of a cutting fluid or other cutting agent migrate to and form a film upon'the surface of the workpiece as it passes beneath the grinding wheel,

I i 9 Claims, 5 Drawing Figures i or. POWER SU PPLY PATENTEU JUL 1 5:914

TANK

Su PPLY D.(L Po'wE 75 FIG ELECTROPHORETIC ASSISTANCE BACKGROUND OF THE INVENTION 1. Field of Invention This invention relates to an arrangement for wet grinding a workpiece, and more particularly to a grinding arrangement in which an electrically conducting workpiece moved against and relative to a suitable grinding element such as a grinding wheel, for example, is flooded adjacent the grinding site with a nonconducting fluid stream containing charged particles of a grinding or cutting agent and subjected to a voltage gradient such that the particles of a grinding or cutting agent entrained in the fluid are attracted to and form a film upon the surface of the workpiece adjacent to the grinding site.

2. Description of the Prior Art It is well known in the grinding art thatthe heat generated at a grinding site during a sustained grinding operation may cause the temperature at'that site to reach levels detrimental to the workpiece or the grind ing wheel, or both. This temperature rise to a harmful level maybe postponed at least for a relatively extended period of time or indefinitely by supplying to the grinding site a substantial quantity of a suitable coolant fluid, for example, water.

Alternatively, it is also well known in the grinding art that the efficiency with which a grinding wheel performs can be considerably improved by supplying to the grinding site a quantity of a grinding or cuttingfluid such as a suitable oil. However,since such oils lack the cooling properties of a coolant fluid such as water, this increased efficiency is accompanied by a rapid rise in temperature to a harmful level.

In order to combine the benefits of these fluids differently affecting grindingoperations, it is widespread practice for many different grinding operations to supply to the grinding site a mixture of a coolant fluid and a grinding or a cutting fluid, for example, one part of a suitable oil to from 20 to 40 parts of water, Thus, some improvement in the efficiency of the grinding operation due to the presence of the cutting fluid is achieved under favorable relatively low temperature conditions maintained by the coolant fluid.

A further improvement inefficiency,- still accompanied by favorable relatively low temperature conditions, has been achieved by delivering the combination of oil and water separately to the grinding site, for exmp e, P9[E. .Qf O l. .q lirs s at hig v ty through very small nozzles to the surface of the grinding wheel adjacent to the grinding line, and 40 parts of water delivered at very low velocity through a large nozzle to the surfaceof the workpiece. For further particulars see Wagner et al US. Pat. No. 2,434,679 issued Jan. 20, 1948. This system necessarily poses one of two problems, either a requirement for sustained fresh supplies of oil and water, or, alternatively, a requirement for a relatively complex fluid separating means illustrated in FIG. l 4 of the patent, effective to separate the oil and water for recirculation through the respective separate nozzle assemblies.

In contrast to the separate fluid delivery systems and the complementary fluid separating means required by the apparatus described above, the instant invention accomplishes substantially the same separation of cool- I METHOD AND MEANS OF GRINDING WITH I 2 t ant and cutting fluids at the grinding site relying solely on an electric field.

In order to remove stock more efficiently from materials relatively hard to grind such as hard metal alloys and carbides, various systems for electrolytically assisted grinding have been devised, typically including provisions for delivering a relatively heavy electric current across the narrow space maintained by nonconducting abrasive particles between a negatively charged electrically conducting bond portion of a grinding wheel and a positively charged electrically conducting workpiece. This substantial electric current is carried by an electrically highly conductive electrolyte such as a suitable salt'solution.

In one such electrolytically assisted grinding system, the flow of a large current to the: workpiece is facilitated by a conducting shoe having a relatively large surface conforming to the surface of the workpiece and insulated therefrom by nonconducting particles in a manner similar to the manner in which the workpiece is insulated from the conducting portion of the grinding wheel. The electrolyte may either be delivered to the spacexbetween the shoe and the workpiece from a source adjacent to the shoe,or be delivered to a chamber within the shoe and thence through perforations in its face adjacent to the workpiece. See Blake U.S. Pat. No. 3,285,843 issued Nov. 15, I966.

The apparatus described above is effective to assist in the removal of stock from a positively charged workpiece, while the instant invention is effective to deposit a film of a cuttingagent upon the surface to be ground of a workpiece.

In another such electrolytically assisted grindingsystern, the electrical circuit is operative periodically to reverse the flow of current to interrupt the deplating action on the workpiece and instead to deplate metal build up on the grinding wheel and to dress the conductive metal bond portion of the grinding wheel. See Kistler US. Pat. No. 2,920,026 issued Jan. 5, I960.

The reversal of the electric current periodically in the apparatus described above is effective to produce deplating and dressing of the grinding wheel alternately with stock removal from the workpiece,while reversal of the voltage gradient in the instant invention is effective alternately to deposit a film of cutting field on the surface to be ground of a workpiece during a grinding operation, and to remove a cutting fluid, from the surface of a workpiece after the grinding operation is completed.

SUMMARY OF THE INVENTION The instant invention contemplates in a grinding machine a method and apparatus wherein an electric field established between an electrode and a workpiece to be ground is effective during a grinding operation to cause the migration of particles of a cutting agent entrained in a coolant fluid to form a film composed of the particles of a cutting fluid or other cutting agent upon the surface to be ground of a workpiece.

The instant invention also contemplates in a grinding machine a method and means'of removing the film of a cutting fluid from the surface of a. workpiece by reentraining the particles of a cutting fluid in the coolant fluid after a grinding operation is completed.

An object of the present invention is the provision of simple and effectivemeans operative during a grinding operation to separate particles of a cutting fluid or other cutting agent from a coolant fluid in which they are entrained, and to deposit upon the surface to be ground of a workpiece a film composed of the particles of a cutting fluid or other cutting agent previously entrained in the coolant fluid.

Another object is the provision of means operative after a grinding operation to reentrain in a coolant fluid a film of cutting fluid deposited upon the surface of a workpiece.

Still another object is the provision of a method for depositing upon the surface to be ground of a workpiece a film formed from particles of a cutting fluid previously entrained in a stream of coolant fluid, and for removing the film of cutting fluid after a grinding operation is completed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation of a simplified schematic representation of the preferred embodiment of the instant invention applied to a surface grinding machine,

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1 comprising a simplified schematic representation of a conventional surface grinder generally designated by the reference numeral 10, a motor driven shaft 11 supports a grinding wheel 12 for vertical feeding movement relative to a workpiece 14.

and for counterclockwise rotation as seen in FIG. 1. The grinding wheel is enclosed by a conventional wheel guard 15 and the workpiece 14 is supported upon a workpiece supporting table 16 reciprocated and transversely fed by means not illustrated, since they are well known in the art and form no part of the instant invention. The wheel guard 15 supports two or more fluid discharge nozzles 17 and an electrode 21 shown as comprising a generally rectangular flat plate with a central opening 22 therethrough to accommodate the peripheral portion of the grinding wheel 12 positioned to engage the surface of the workpiece 14. The electrode 21 may be supported adjacent to but spaced from the workpiece 14 by a supporting assembly on at least one side of the wheel guard 15, including an electrically insulating block 24 secured to the wheel guard 15, a pair of supporting rods 25 each secured at one end to the electrode 21, and a pair of locking screws 26 each threadably engaging the insulated block 24 and operative to secure one of the supporting rods 25 against movement relative to the insulating block 24. If used, a second electrode supporting assembly on the other side of the wheel guard 15, not shown in FIG. 1, preferably is generally similar if not identical to the first electrode supporting assembly illustrated in FIG, 1.

The coolant fluid of the instant invention and the particles of a cutting fluid or other cutting agent entrained therein are supplied to the space between the workpiece 14 and the electrode 21 by two or more nozzle assemblies 17 connected through conduits 31 and pump assembly 32 to a tank 33, also connected through return conduit 34 and pump 35 to an open tray 36 located beneath the reciprocating table 16 to collect and return the combined fluid to the tank 33 for recirculatron.

The direct current power supply .41 is connected through switch assembly 42 to the workpiece 14 and the electrode 21 so that the workpiece is charged positively and the electrode is charged negatively when the switch assembly 42 is in its on position. The switch assembly 42 is selectively movable to an off position in which the workpiece and the electrode are disconnected from the power supply and to a reverse position in which the workpiece 14 is connected to the negative side of the power supply and the electrode 21 is connected to the positive side of the power supply.

During a grinding operation, the pump 32 is operated at a rate sufficient to deliver from nozzles 17 a stream of coolant fluid and entrained negatively charged particles of a cutting fluid or other cutting agent, for example, droplets of an emulsified oil sufficient to substantially fill the space between the surface to be ground of the workpiece l4 and the electrode 21. With the switch assembly concurrently positioned in its on position there is created an electromotive force between the workpiece 14 and the electrode 21 effective to cause the negatively charged droplets of an emulsifiedoil, to migrate to the surface to be ground of a positively charged workpiece 14, where these droplets collect to form a thin film, not shown inFIG. 1, which passes between the surface of the workpiece 14 and the grinding wheel 12 as the workpiece is reciprocated beneath the grinding wheel. Such migration of the charged particles is characteristic of the process known as electrophore- SIS.

When the grinding operation is completed, the switch assembly 42 may be moved to its open position to deenergize the-workpiece l4 and the electrode 21, thereby allowing the stream of coolant fluid passing over the workpiece 14 to reentrain and remove the droplets of oil which have formed the film on the surface of the workpiece during a grinding operation. Alternatively, when the grinding operation is over, the switch assembly 42 may be moved to its reverse position so that the workpiece 14 is negatively charged and the electrode 21 is positively charged, thus encouraging the movement of the oil droplets away from the surface of the workpiece with the. stream of coolant fluid.

The improvement in the effectiveness of a grinding operation due to electrophoretic assistance, that is by the application of electrophesis, is indicated in the following table by the increase in the grinding ratio for electrophoretic grinding performed with the grinding wheels specified at various different voltage levels, as compared to the grinding ratio achieved by conventional grinding operations performed with the. same grinding wheels on the same material under otherwise corresponding operating conditions. The grinding ratio as used here is the ratio of the pounds per hour of metal removed to the cubic inches per hour of grinding wheel wear during a grinding operation.

TABLE 1 Hard Huron Die Steel Process Used Grinding Ratio, G, With Applied Voltage of Wheel Specification No. 302 Stainless Steel Process Used Grinding Ratio, 0, With Applied Voltage of Wheel Specification Conventional 7.03 10.28 (32A461-J8VBE) 7.69 9.03 Average 7.36 9.65

32 i so Electrophoretic 13.06 16.33 (32A461-JSVBE) 11.03 15.86 Average 12.04 16.10 (+62%) (+67%) Conventional 11.35 8.47 (32A46lL8VBE) 11.06 7.72

Average 11.20 8.10

Electrophoretic 15.44 15.49 (32A46l-L8VBE) 15.05 11.27 Average 15.25 13.38 '(+36/z) (+65%) Conditions for the comparative grinding tests summarized in Table 1 above were'as follows:

Machine U sed Norton S-3 Surface G rinder Material Used- Hurton die steel. RHC59. 1.995 x 1 Down-feed-0.00l or 0.002/com'plete cross-fe Totaldown-feed.0.020/run Coolant-WHEELMATE No. 803*. 1/20 parts water Dressing- Diamond. initially only Traverse -600"/min. v

with water to form a stable emulsion.

From consideration of the respective grinding ratios achieved while grinding Hard Huron Die Steel, itwill be evident the grinding ratio is improved in this instance by from 15 to 26 percent when electrophoretic grinding is used. Similarly, from consideration of the grinding ratios achieved .while grinding relatively harder No. 302 Stainless Steel it will be apparent that the grinding ratio is increased by from 35 to 67 percent when electrophoretic grinding is used. Thus, the results disclosed in Table 1 aboveindicate that the beneficial effect of electrophoretic grinding increases in direct proportion to the relative hardness and consequently the relative difficulty encountered in grinding various different materials by conventional grinding means.

i Referring now to FIG. 2, the instant invention is shown applied to a simplified schematic representation of a cylindrical grinding machine including a grinding wheel 12 supported on and rotated clockwise by a drive shaft driven by a wheel drive motor not shown, a workpiece 14 rotated counterclockwise at a relatively much lower rate by a work drive motor not shown, at least one nozzle 17 for delivering a stream of coolant fluid with entrained particles of a cutting fluid, and electrode 21 having a portion thereof conforming to but spaced a uniform short distance from the surface of the workpiece 14, and an electrically insulated block 24 supporting the electrode 21. In this configuration as in that illustrated in FIG. 1, the workpiece 14 may be connected to the positive terminal and the electrode 21 may be connected to the negative terminal of a direct current power supply, so that negatively charged particles of a cutting fluid, such as an emulsified oil, migrate through the coolant fluid to the surface of the positively charged workpiece 14 to form a film which passes between the grinding wheel 12 and the workpiece 14 as the workpiece is' ground.

Referring next to FIG. 3, the instant invention is shown applied to a simplified schematic representation of a centerless grinding machine including a grinding wheel 12 supported on and rotated clockwise by a drive shaft driven by a wheel drive motor not shown, a workpiece 14 rotated counterclockwise on a work rest blade 51 at a relatively lower rate by a regulating wheel 52 rotated clockwise by a wheel drive motor not shown, at least one nozzle 17 for delivering a stream of coolant fluid with entrained particles of a cutting fluid, electrode 21 having a portion thereof conforming to but spaced a uniform short distance from the surface of the workpiece l4, and an electrically insulated block 24 supporting the electrode 21. A

In this configuration as in those illustrated in FIGS. 1 and 2, the workpiece 14 may be connected to the positive terminal and the electrode 21 may be connected to the negative terminal of a direct current power supply, so that negatively charge particles of a cutting fluid, such as an emulsified oil, migrates through the coolant fluid to the surface of the positively charged workpiece 14 to form a film which passes between the grinding wheel 12 and the workpiece 14 as the workpiece is ground.

Referring here to FIG. 4, an alternative embodiment of the instant invention is shown applied to a simplified schematic representation of a centerless grinding machine including a grinding wheel 12 supported on and rotated clockwise by a drive shaft driven by a wheel drive motor not shown, an elongated workpiece 14 supported upon a work rest blade 51 and rotated counterclockwise at a relatively lower rate by a regulating wheel rotated clockwise by a drive motor not shown, at least two nozzles 17 fordelivering streams of coolant fluid with entrained particles of a cutting fluid, electrode 21 having a portion thereof conforming to but spaced a uniform short distance from the surface of the workpiece l4, and an electrically insulated block 24 supporting the electrode 21.

In this configuration as in those illustrated in FIGS. 1, 2 and 3 the workpiece 14 may be connected to the positive terminal and the electrode 21 may be connected to the negative terminal of a direct current power supply,'so that negatively charged particles of a cutting fluid, such as emulsified oil, migrate through the coolant fluid to the surface of the positive charged workpiece 14 to form a film which passes between the grinding wheel 12 and the workpiece 14 as the workpiece is ground. In addition, because of the relative dispositions sequentially of the electrode 21, the work rest blade 51, and the line of contact between the grinding wheel 12 and the workpiece 14, the film of cutting fluid deposited upon the surface of the workpiece passes across and thereby lubricates the working'edge of the work rest blade to reduce or eliminate blade wear.

It will be obvious the film of a cutting agent deposited upon a surface to be ground of a workpiece, which actually passes beneath the grinding wheel, will be ground away. However, in many grinding machine, workpiece, electrode configurations, the film will be redeposited on portions of the workpiece surface already ground. For example, see one such configuration in FIG. 1.

Accordingly, the operation of the apparatus illustrated in FIG. 1, as described, includes interruption or reversal of the connections to the power supply 41, by operation of switch assembly 42 after the grinding v operation is completed to provide for at least partial removal of the residual film on the ground workpiece.

The same capability for at least partial removal of residual film may be provided, as necessary, in any of the configurations illustrated in FIGS. 2, 3 and 4 by connecting the workpiece l4 and the electrode 21 to the power supply 41 through a switch assembly 42 as shown in FIG. 1.

In a grinding machine configuration in which a ground workpiece is moved rapidly away from the grinding wheel, as in FIG. 4, the electrode 21 may be substantially elongated to extend the length of the discharged workpiece, that is to the right in FIG. 4, for example, and additional nozzles 17 may be used to distribute the fiuid stream along the length of the discharged workpiece, so that reversal of the electrical connections to the workpiece and the electrode after the workpiece has passed over the work rest blade 51 shown in FIG. 4 will be effective to remove at least a portion of the residual film from the discharged workpiece.

The electrical connections shown schematically in FIG. 1 as connected directly to the workpiece 14 and the electrode 21 may alternatively be connected indirectly thereto through electrically conducting elements associated therewith, for example, through the table 16 supporting the workpiece 14 or through a rod 25 connected to the electrode 21.

The specific means of coupling the electrical connection to the workpiece 14 in each of the grinding machine configurations shown in FIGS. 2, 3 and 4 is not shown, because the details of such connections form no part of the instant invention. However, it will be apparent such connection may be made through any type of electrically conducting supporting means for the workpiece such as an assembly including a workpiece center or a face plate with clamping jaws.

Alternatively, the coupling may be made directly to a rotating workpiece through a brush or shoe assembly maintained in electrically conducting sliding engagement with the surface of the workpiece. In fact, in order to maintain the workpiece energized throughout the desired operating cycle, a rotating workpiece may be engaged continuously during the operating cycle by at least one of two or more brush or shoe assemblies respectively located on opposite sides of the grinding wheel 12. Such an arrangement of multiple brush or shoe assemblies would be particularly useful on the grinding machine configuration shown in FIG. 4.

Both in the various configurations illustrated herein and in other applications of the instant invention the single electrode 21 illustrated in each of FIGS. 1 through 4 may be replaced by two or more electrodes cooperating with the workpiece 14. For example, the single electrode used on a cylindrical grinder, as shown in FIG. 2, may be replaced with an assembly comprising an electrically insulated arcuately curved supporting segment 24 with spaced radial slots therein, each receiving an arcuately curved electrode 21 substantially conforming to a portion of the surface of the coacting workpiece and positioned radially by an adjustable positioning screw 29 and secured by apair of lock nuts .27 engaging a pair of supporting screws 28 fixedly attached to an insulating insert in the back of the electrode 21. See FIG. 5 for such a unit with electrodes adjustable radially for grinding a range of workpiece diameters.

As indicated in FIGS; 1 through 4, the configuration of the electrode 21 may be varied as necessary to adapt it to various different grinding machine and workpiece configurations, bearing in mind the importance of a favorable voltage gradient in the application of this invention, in contrast to the requirement in electrolytic grinding apparatus for a relatively high current density.

Since a given voltage potential across the power source produces a voltage gradient between the workpiece and the electrode which increases as the distance between the workpiece and the electrode is reduced, it is most efficient to reduce the spacing between the workpiece and the electrode to its practical minimum, allowing for the circulation therebetween of an adequate supply of a coolant fluid with entrained particles of a cutting agent. For example, the configuration of the instant invention illustrated in FIG. 1 has per- As material is removed from a workpiece, widening the space between the workpiece and the electrode, the

supporting means for the electrode may be adjusted to shift the electrode toward the workpiece to again reduce the space between the workpiece and the electrode, and thereby maintain a favorable voltage gradient.

This adjustment of the electrode supporting means may be accomplished manually, for example, by loosening the locking screws 26 shown in FIG. 1 to permit suitable movement of the rods 25 relative to the supportingblock 24, or by loosening the locking nuts 27 on the pair of supporting screws 28 and by adjusting the positioning screw 29 for each electrode 21 shown in FIG. 5.

Alternatively, the electrode 21 may be supported on a steadyrest assembly or other supporting means therefore incorporating means automatically operable to displace the electrode supporting means accordingly as the workpiece is reduced in size during the grinding operation. For example, after a heavy roughing cut on a rough forging, the electrode supporting means could be advanced automatically to 'move the electrode toward the rough ground workpiecepreliminary to a finish grinding pass.

Similarly, while the switch assembly 42 as shown in FIG. 1 is manually operated, it will be apparent this switch assembly can be controlled bya suitable solenoid mechanism or other automatically operable control means actuated in coordinated relation to the completion of the grinding cycle performed by the grinding machine, so that the connectionstothe power supply 41 are either interrupted or reversed automatically afterthe grinding operation is completed.

Recalling the several references above to a cutting fluid or other cutting agent, and more specifically to droplets of an emulsified oil, there are various compositions of oil used as cutting fluids, commercially available from various sources, which can be employed according to the teachings of the instant invention to provide electrophoretic assistance for a grinding operation. For example, WHEELMATE No. 803 available commercially from Norton Company is a sulfochlorinated soluble oil which mixes readily with water to form a stable emulsion. This fluid was used successfully to obtain the test results described in Table I above.

Alternatively, the cutting agent entrained in the coolant fluid for use according to the teachings of the instant invention may consist of dry particles of a suitable lubricant material such as a flourinated hydrocarbon, for example, tetrafluoroethylene. Such particles, which may be either positively or negatively charged, are usu ally positively charged. When such particles, positively charged, are substituted for droplets of an emulsified oil, usually negatively charged, the workpiece must be connected to the negative side .and the electrode must be connected to the positive side of a source of direct current in order to produce a film of such particles on the workpiece during a grinding operation.

Since particles of a fluorinated hydrocarbon are not detached from the surface of a workpiece by interrupting the circuit to the power supply or by reversing the charges on the workpiece and the electrode, the film formed from such particles may be stripped from the surface of the workpiece aftera grinding operation is completed.

While the enclosed drawings show and the accompanying description refers to a grinding wheel, a grinding system including the instant invention may employ other types of grinding elements, for example, an abrasive belt or an abrasive disc.

Theabove description is to be considered as illustrative only rather than as limiting in any sense, and various modifications of grinding systems incorporating the instant invention are contemplated within the scope of the appended claims.'

What is claimed is: i

1. A grinding .system comprising,

a moving grinding element for an electrically conductive workpiece moving against and relative to thegrindingelement,

electrode means spaced and electrically insulated from a surface to be groundof such a workpiece.

an electrically substantially nonconducting liquid stream comprising electrically charged particles of a cutting agent entrained in a coolanc fluid,

means arranged to deliver said liquid stream to the space between the electrode means and such a workpiece. and I a source of direct electrical current operatively connected to maintain the electrode means and such awqr s iss snqs telxsllqs dh e i y charged particles of a cutting agent being attracted to such a workpiece. whereby a film of the cutting agent is deposited by electrophoresis upon a surface to be ground of such a workpiece.

2. grinding system as described in claim 1,

wherein said particles of a cutting agent are negatively charged droplets of oil emulsified in the cooling fluid, and

, wherein said source of direct electrical current is operatively connected to maintain the electrode means negative and to maintain such a workpiece P i I 3. A grinding system as described in claim 2 and, in addition,

means operative after a grinding operation is completed to disconnect said source of direct electrical current from such a workpiece.

whereby the liquid stream is effective to reemulsify the droplets of oil in the coolant fluid from the surface of such a workpiece.

4. A grinding system as described in claim 2 and, in

addition,

means operative after a grinding operation is completed to reverse the polarity of the electrode sdstsse an rkp sse whereby the oil droplets collected on the surface of such a workpiece are rapidly returned to the liquid stream. d

5. A grinding system as described in claim 1,

wherein said particles of a cutting agent are a fluorinated hydrocarbon.

6. A grinding system as described in claim 1,

wherein said particles of a cutting agent are tetratluoroethylene.

7. A method of grinding an electrically conductive workpiece, comprising,

moving a grinding element,

moving an electrically conductive workpiece against and relative to the grinding element,

supporting an electrode means spaced'and electrically insulated from the surface to be ground of a workpiece,-

delivering to the space between the electrode means and a workpiece an electrically substantially nonconducting liquid stream containing electrically chargedparticles of a cutting agent entrained in a cooling fluid,

connecting a source of direct electrical current so as to maintain the electrode means and a workpiece oppositely so charged that the electrically charged particles of a cutting agent are attracted to a workpiece, whereby the grinding operation is performed under a film of the cutting agent deposited by electrophoresis upon the surface to be ground of a workpiece. 8. A method of grinding an electrically conductive workpiece as described in claim 7, and further comprisdisconnecting the source of direct electrical current so as to deenergize a workpiece, whereby the particles of a cutting agent forming a film upon the surface of a workpiece are reentrained in the liquid stream.

9. A method of grinding an electrically conductive workpiece as described in claim 7, and further comprismg,

v reversing the connections to a source of direct electrical current so as to reverse the charges upon the electrode means and a workpiece,

whereby the particles of a cutting agent forming a film upon the surface of a workpiece are detached therefrom and reentrained in the liquid stream. 

1. A grinding system comprising, a moving grinding element for an electrically conductive workpiece moving against and relative to the grinding element, electrode means spaced and electrically insulated from the surface to be ground of the workpiece, an electrically substantially nonconducting liquid stream comprising electrically charged particles of a cutting agent entrained in a coolanc fluid, means arranged to deliver said liquid stream to the space between the electrode means and the workpiece, and a source of direct electrical current operatively connected to maintain the electrode means and the workpiece oppositely charged, the electrically charged particles of a cutting agent being attracted to the workpiece, whereby a film of the cutting agent is deposited by electrophoresis upon the surface to be ground of the workpiece.
 2. A grinding system as described in claim 1, wherein said particles of a cutting agent are negatively charged droplets of oil emulsified in the cooling fluid, and wherein said source of direCt electrical current is operatively connected to maintain the electrode means negative and to maintain the workpiece positive.
 3. A grinding system as described in claim 2 and, in addition, means operative after a grinding operation is completed to disconnect said source of direct electrical current from a workpiece, whereby the liquid stream is effective to reemulsify the droplets of oil in the coolant fluid from the surface of the workpiece.
 4. A grinding system as described in claim 2 and, in addition, means operative after a grinding operation is completed to reverse the polarity of the electrode means and of a workpiece, whereby the oil droplets collected on the surface of the workpiece are rapidly returned to the liquid stream.
 5. A grinding system as described in claim 1, wherein said particles of a cutting agent are a fluorinated hydrocarbon.
 6. A grinding system as described in claim 1, wherein said particles of a cutting agent are tetrafluoroethylene.
 7. A method of grinding an electrically conductive workpiece, comprising, moving a grinding element, moving an electrically conductive workpiece against and relative to the grinding element, supporting an electrode means spaced and electrically insulated from the surface to be ground of a workpiece, delivering to the space between the electrode means and a workpiece an electrically substantially nonconducting liquid stream containing electrically charged particles of a cutting agent entrained in a cooling fluid, connecting a source of direct electrical current so as to maintain the electrode means and a workpiece oppositely so charged that the electrically charged particles of a cutting agent are attracted to a workpiece, whereby the grinding operation is performed under a film of the cutting agent deposited by electrophoresis upon the surface to be ground of a workpiece.
 8. A method of grinding an electrically conductive workpiece as described in claim 7, and further comprising, disconnecting the source of direct electrical current so as to deenergize a workpiece, whereby the particles of a cutting agent forming a film upon the surface of a workpiece are reentrained in the liquid stream.
 9. A method of grinding an electrically conductive workpiece as described in claim 7, and further comprising, reversing the connections to a source of direct electrical current so as to reverse the charges upon the electrode means and a workpiece, whereby the particles of a cutting agent forming a film upon the surface of a workpiece are detached therefrom and reentrained in the liquid stream. 